1. Field of the Invention
The present invention relates to disk drives for computer systems. More particularly, the present invention relates to a disk drive employing a constant contact inertial latch.
2. Description of the Prior Art
A computer system usually includes one or more disk drives for economical, non-volatile data storage. Prior art disk drives typically comprise a base for housing a disk and a head attached to a distal end of an actuator arm. A spindle motor rotates the disk about its axis, and a voice coil motor (VCM) rotates the actuator arm about a pivot in order to position the head radially over the disk. While the disk drive is powered down the head is typically parked in order to protect the data recorded on the disk as well as prevent damage to the head. The head may be parked on a landing zone on the inner diameter (ID) of the disk, or alternatively, the head may be parked on a ramp located at the periphery of the disk (a.k.a., ramp loading/unloading). If parked on a landing zone, the disk drive typically employs a magnetic latch to help retain the head in the parked position when the disk drive is subject to a physical shock, particularly a rotational shock. The magnetic latch typically comprises a magnet attached or embedded into a crash stop for latching onto a tang extending from a base end of the actuator arm. If the head is parked on a ramp, the frictional force of the ramp helps retain the head in the parked position. However, in either case if the force of a rotational shock exceeds the latching force of the magnetic latch or the frictional force of the ramp, the actuator arm will “unlatch” causing the head to fly over the data area of the disk.
In prior art disk drives an inertial latch has been employed which prevents the actuator arm from unlatching when the disk drive is subject to large rotational shocks. The inertial latch comprises a protruding arm having an inertia which causes it to rotate about a pivot and “catch” the actuator arm to prevent it from unlatching during a rotational shock. The inertial latch also comprises a biasing mechanism (e.g., a spring) for applying a biasing force to the arm in order to reposition it when the rotational shock subsides. However, it is difficult to design an inertial latch that will rotate and catch the actuator arm before it unlatches under all circumstances. That is, depending on the character and magnitude of the rotational shock the inertial latch may not rotate in time to catch the actuator arm, particularly when the disk drive is subject to smaller rotational shocks sufficient to defeat the force of a magnetic latch or frictional force of a ramp. A larger magnet having an increased latching force may be employed to compensate for smaller rotational shocks, but this requires a more expensive VCM with sufficient torque to unlatch the actuator arm when the disk drive is powered on.
There is, therefore, a need for a disk drive which cost effectively prevents the actuator arm from unlatching when the disk drive is subject to physical shocks while powered down.